Merosaurus

<i>Dornraptor</i>

Dornraptor

Genus of theropod dinosaurs

Dornraptor (meaning "Dorset robber or thief") is a genus of averostran theropod dinosaur from the Early Jurassic (Late Sinemurian stage, around 194-192 million years ago) of Charmouth, Dorset. It was described as coming have come from the Blue Lias Formation, although some authors considered it to come from Charmouth Mudstone Formation.[1] It was considered either a tetanuran or a ceratosaurian, and lived in what is now England, along other theropod taxa like like Dracoraptor and Sarcosaurus.[2]

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History of discovery

The holotype was discovered on or before 1847.[citation needed] It and a referred specimen were originally by Richard Owen used as part of the type material of the thyreophoran Scelidosaurus. Subsequent studies have reconsidered their classification, suggesting instead that they represent one or more theropods rather than an early ornithischian. For Scelidosaurus, a replacing neotype was assigned. The informal name "Merosaurus newmani", was coined by Samuel Paul Welles, H.P. Powell, and Stephan Pickering in 1995 in an unpublished manuscript for the theropod material.[3] Carrano and Sampson (2004) proposing that the articulated knee joint likely belonged to a basal, indeterminate tetanuran theropod and Darren Naish and David Martill (2007) also assigned these specimens to Tetanurae.[2][4][5]

In 2010 Roger Benson suggested that the articulated femur, tibia, and fibula could be attributed to Coelophysoidea, while ultimately concluding that both specimens were indeterminate theropods.[6] In 2024, the material was formally described by Matthew G. Baron as a new genus and species of averostran theropod, Dornraptor normani. The generic name, Dornraptor, combines "Dorn", an abbreviated form of the Anglo-Saxon Dornwaraceaster—referring to the English region of Dorset—with the Latin word "raptor", meaning "robber" or "thief", which is frequently used in the names of small- and medium-sized theropods. The specific name, normani, honours British palaeontologist David B. Norman.[2]

Description

Illustration of the articulated Dornraptor holotype, including the missing fibula

Dornraptor is known from two specimens. The holotype, BMNH 39496, consistst of the articulated distal end of a right femur and a proximal third of a right tibia, with an associated right fibula (now lost). GSM 109560, a partial left femur, was also referred to the genus. Dornraptor stands out from other theropods due to a large scar along the medial side of the distal end of the femur, a medial distal crest, and a prominent anterior trochanter separated from the head by a cleft. Additionally, it possesses a shallow trochanteric shelf and a foramen on the anterior surface of the femur. Its femur also features a deep anterior sulcus between the articular condyles and a medial condyle with similar anteroposterior diameter to the width of the articular surface. Dornraptor exhibits an elongated cnemial crest reaching proximally beyond the medial and lateral condyles, along with a pronounced fibular crest extending up to the proximal end of the tibia. The lateral side of the tibia also displays a sharp crest parallel to the fibular crest, forming a distinct bulge distally. Additionally, the proximal end of the tibia shows a separate crest, not connected to the fibular crest, and a noticeable cleft between the posterior condyles. Lastly, the lateral condyle of the tibia forms an acute angle when viewed from the medial side.[2]

Classification

While specimens BMNH 39496 and GSM 109560 lack anatomical overlap, their discovery in the same stratigraphic unit, along with similar size and proportions, suggests they belong to the same taxon, distinct from earlier forms and contemporaneous taxa like Dracoraptor and Sarcosaurus. Utilizing a modified version of the Baron et al. (2017) phylogenetic dataset,[7] Dornraptor was found to be an early-branching averostran theropod in a polytomy with Elaphrosaurus, Cryolophosaurus, and the clade containing Allosaurus and Piatnitzkysaurus. This clade was recovered as the sister group to a clade containing the ceratosaurs Eoabelisaurus and Ceratosaurus. These results are displayed in the cladogram below, with Dornraptor and the contemporary non-averostrans Dracoraptor and Sarcosaurus in bold:[2]

Theropoda

Scoring Dornraptor in other matrices also resulted in its placement in various basal positions within the Averostra, outside of the major clades Abelisauroidea and Coelurosauria.[2]

References

  1. [1]
    Choiniere, Jonah N.; Wills, Simon; Bennett, S. Christopher; Barrett, Paul M. (2020). "A small theropod dinosaur from the Lower Jurassic Lias Group of Charmouth, Dorset". Proceedings of the Geologists' Association. 131 (6): 751–757. doi:10.1016/j.pgeola.2020.08.003. ISSN 0016-7878.
  2. [2]
    Baron, Matthew G. (2024-04-29). "A new name for old bones: A reassessment of Early Jurassic theropod remains from Dorset, England". Palaeontologia Electronica. 27 (1): 1–12. doi:10.26879/1346. ISSN 1094-8074.
  3. [3]
    Mortimer, M (2004) "The Theropod Database" Archived 2013-09-29 at the Wayback Machine. University of Washington. Retrieved 2007-07-04.
  4. [4]
    Carrano, Matthew T.; Sampson, Scott D. (2004-09-27). "A review of coelophysoids (Dinosauria: Theropoda) from the Early Jurassic of Europe, with comments on the late history of the Coelophysoidea". Neues Jahrbuch für Geologie und Paläontologie - Monatshefte. 2004 (9): 537–558. doi:10.1127/njgpm/2004/2004/537. ISSN 0028-3630.
  5. [5]
    Naish, Darren; Martill, David M. (2007). "Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia". Journal of the Geological Society. 164 (3): 493–510. doi:10.1144/0016-76492006-032. ISSN 0016-7649.
  6. [6]
    Benson, Roger B. J. (2010-03-15). "The osteology of Magnosaurus nethercombensis (Dinosauria, Theropoda) from the Bajocian (Middle Jurassic) of the United Kingdom and a re-examination of the oldest records of tetanurans". Journal of Systematic Palaeontology. 8 (1): 131–146. doi:10.1080/14772011003603515. ISSN 1477-2019.
  7. [7]
    Baron, Matthew G.; Norman, David B.; Barrett, Paul M. (2017). "A new hypothesis of dinosaur relationships and early dinosaur evolution". Nature. 543 (7646). London: Nature Research: 501–506. Bibcode:2017Natur.543..501B. doi:10.1038/nature21700. ISSN 0028-0836. PMID 28332513. S2CID 205254710.
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